Avalanche Forecast
Regions: Mt Hood.
Loose avalanches, particularly loose wet avalanches, may release naturally or be human triggered as the sun comes out Sunday. Take care around terrain traps that would amplify the consequences of a small avalanche. Older wind slabs are becoming less reactive but still exist in specific areas above treeline.
Discussion
Snow and Avalanche Discussion
Mt. Hood storm totals through Friday night tallied 12-15" over the last few days. Temperatures have remained cold and there has been more cloud than sun over this period, minimizing aspects affected by the March sun.
Natural winds slabs were reported in White River Canyon Saturday on east aspects above treeline, likely releasing within the last 24 hours and estimated to be 1-2' deep. In very steep non-wind and shaded terrain, loose dry avalanches were running fast and far. Â
Snowpack Discussion
March 4, 2019
Here we are at the beginning of March. The days are noticeably longer, the sun feels warmer, but the winter is far from over. This may be a good time to take stock of February’s events, where we are now, and what we might expect in the future.
A February to Remember
Many longtime Cascade travelers continue to remark about the long span of high-quality travel conditions in February. Indeed, we’ve experienced three weeks of very cold and snowy conditions. Backcountry travelers frequently reported, “best conditions in yearsâ€. February also saw a few rounds of natural and human triggered avalanches. These avalanches were different from our more frequent Cascade storm slabs; here today and gone tomorrow. Most avalanches failed on buried weak persistent layers. As such, most zones spent much of February with Persistent or Deep Persistent Slabs in their forecasts.
Natural avalanche in Icicle Creek Feb 13, 2019. Photo: Matt Primomo
With the notable absence of high elevation rain events, snowpacks around the northwest grew remarkably. On the west slope, most weather stations added 2-4 ft of snow depth. East-side locations added 1-2 ft. Mt Hood locations added 4-5 ft. Even with these impressive snowpack growths, many Cascade Snotel sites are recording near or just below average snow depths for the winter. Â
During most of February, snow conditions were soft and powdery making for fun recreating in many areas. Photo Matt Primomo.
Where We Are Now
Lack of avalanche activity on the layer of buried facets from Feb 8 allows us to gain confidence in many areas. In many areas, there has been a lack of avalanche activity and snowpack tests have been less reactive. These two pieces combined have allowed us to drop persistent slabs from some forecasts and shift others to “unlikely.†The exception is the East Cascades where a shallow snowpack has preserved buried facets, and persistent slabs will remain possible until the sensitivity drops further. So, we’re out to the woods, right? Well, maybe. The same cold and stormy weather that brought us excellent snow quality, also allowed us to bury new weak layers. So far we haven’t confirmed any avalanches on these shallow weak layers, but they have our attention and we’re tracking them.
Recently our attention shifted to the upper snowpack. Recent avalanche problems have largely focussed on wind transported snow. Several wind events, predominantly from the east, placed wind slabs on a variety of aspect. With the colder than normal temperatures, wind slabs may not heal as quickly as normal.
A small natural wind slab avalanche in the Crystal Mt backcountry. Photo; Dallas Glass
What Might We Expect
As we move into March, it’s anyone’s guess what specific weather patterns lay in store of us. However, there are two items that stick out in our minds.
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The strength of the March sun: You can already feel it just walking around town. As the sun creeps higher into the sky and the days grow longer, the sun can have a greater impact on the snow surface. When the sun comes out, expect things to change quickly. You may see avalanches conditions change with natural loose avalanches originating from sunny slopes, surface snow becoming thick and heavy, and slabs taking on a moist to wet snow character.Â
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High elevation travel: Frequently March begins to usher in a period where we push higher and deeper into the mountains. Remember, we don’t have as much information about these far-flung locations. If you use the longer days of March to travel to bigger objectives, keep your eyes open. When observations don’t line-up with the avalanche advisory, you may be experiencing a different snowpack. It’s times like these we need to stop and reevaluate.
Mt Baker on a nice day in early February. Photo: Lee Lazzara
February was amazing! but March is here… there’s still plenty of winter left. Stay safe out there.
Avalanche Problems
Loose Wet
With sunny skies and milder temperatures forecast Sunday, loose wet avalanches are most likely to release from steep, rocky, sunny slopes as the day progresses. Monitor changes in the upper snowpack, looking for natural pinwheels or small loose wet avalanches as clear signs of increasing danger. Avoid terrain traps like gullies where even a small avalanche can bury you. There has been enough recent snowfall that these avalanches might become large enough to do serious damage even without a terrain trap.
In the same vein, on very steep shaded slopes loose dry avalanches still have the potential to run fast and far.
Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Several loose wet avalanches, and lots of pinwheels and roller balls.
Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.
Aspects: East, South East, South, South West, West.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 1
Wind Slabs
You may still find winds slabs lingering above treeline on steep wind loaded aspects. Debris from natural wind slab avalanches were observed Saturday in White River Canyon on east aspects above treeline. It's been cold so wind slab instabilities will take longer than usual to stabilize.
Approach steep unsupported slopes with wind-drifted snow cautiously, feeling for firm or hollow sounding snow as a sign that wind slabs may be present. You can stay safe by traveling on ridges, wind-scoured areas and any slope less than 35 degrees.
Release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..
Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.
Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.
Aspects: All aspects.
Elevations: Alpine.
Likelihood: Possible
Expected Size: 1 - 1